1. Field of the Invention
The present invention generally relates to rotary magnetic couplings, also known as magnetic drives or magnetic clutches, and more particularly to an inner magnet assembly having an inner ring body with magnet guides, magnets and an overlying sleeve.
2. Discussion of the Prior Art
In many rotating devices such as pumps, it is desirable to avoid potential seal leakage by not using seals in conjunction with rotating parts. Accordingly, it has become more common to employ a magnetic drive system to eliminate the need for seals along rotating surfaces. While such devices may still employ static seals, because of their lack of dynamic or rotational seals, they have become known as “sealless”. Indeed, magnetic drive structures have been used in the design of various pumps, including positive displacement gear pumps. Magnetic couplings or drive systems also may be used for example, in devices such as mixers, valves, compressors, clutches, and the like.
In prior art magnetically driven devices, it is common to have an inner magnet assembly with preselected magnets affixed to an inner ring and sealed from exposure to foreign fluids or gases to protect the magnets. The magnets typically are flat or bar-shaped and are substantially planar or arcuate, and are chosen to correspond in strength and number to the magnets on a complementary outer magnet assembly of the magnetic coupling. It is common for the inner magnet assembly to be referred to as the driven magnet, such as when an outer magnet assembly is connected to a rotational power system, such as an electric motor, and is referred to as the drive magnet.
The inner ring of prior art devices also may have slots about its periphery to locate the bar shaped magnets. However, the slots tend to be of the same depth throughout their length, with side walls covering significant portions of the sides of the magnets. This reduces the effectiveness of the magnetic coupling. This, in turn, tends to require the use of stronger or larger, more expensive magnets for a given torque capacity. The selection of magnets dictates the torque capacity of the magnetic drive assembly, and it is important to match the torque capacity of a device to the requirements for the device in order to manufacture and operate the device with as little heat generation and as efficiently as possible.
Once chosen, the magnets of the prior art devices normally are affixed to the inner ring using conventional fasteners, such as rivets or the like, or by using adhesives, such as epoxy or the like. In addition to being affixed in a relatively permanent manner to the inner ring, the magnets often are isolated from their immediate environment by the application of a sealant, a shrink wrap or comparable material to avoid corrosion or other ill effects. In some instances, protection of the magnets is achieved by a sleeve that is welded at each end to the inner ring to permanently seal the magnets within the assembly. However, use of fasteners, difficult to handle substances, such as epoxy, or other substances used to mount the magnets are not desirable from a cost and ease of manufacturing standpoint. Similarly use of shrink wraps, epoxy or other sealants, or welding of metallic sleeves to seal the magnets from the immediate environment also are not desirable. Moreover, the relatively permanent nature of the affixation of the magnets to the inner ring or welding of a sleeve results in a given prior art inner magnet assembly having a torque capacity that essentially is fixed, with the assembly not being easily reconfigurable for use in alternative applications having different torque capacity requirements.
Accordingly, it is desirable to simplify the manufacturing of inner magnet assemblies by removing the use of adhesives and sealants. It would be advantageous to eliminate the messy and more complicated permanent affixation of the magnets to the inner ring. While one may choose, to some extent, to use sealants or welding to seal the magnets from the environment, it would be advantageous to be able to eliminate them as well. It also is desirable to reduce the covering of the side walls of the magnets by the locating slot side walls, so as to be able to use smaller, thinner, less powerful or generally less expensive magnets to achieve a comparable magnetic coupling. In addition, it would be highly advantageous to be able to make an inner magnet assembly which can be readily reconfigured in terms of the selection of the number and strength of the magnets used, so as to be able to adapt devices to users changing needs, as opposed to having to replace the entire magnetically coupled device or the entire inner magnet assembly.
The present invention addresses shortcomings in prior art inner magnet assemblies, while providing the above mentioned desirable features.